In financial self-service equipments, for verifying sheet-type valuable documents (such as banknotes, checks, bills of exchange) processed in batches one by one, a whole stack of sheet-type valuable documents are required to be separated from each other one by one. And then identification means such as image identification, thickness detection and magnetic information detection are performed on the separated individual sheet-type valuable documents, to ensure that a newness degree and authenticity of the sheet-type valuable documents that are processed meet the requirements. The thickness detection is a critical module which is indispensable in the whole detection. The main function of the thickness detection device is to detect thickness signals of a passing sheet-type medium, and determine, according to the thickness signals, a new and old degree of the sheet-type valuable document processed, whether a foreign matter is adhered to the surface of the valuable document and the like. It may be further determined whether the valuable document separated by the machine is a single sheet, i.e., whether the separated banknote is actually two banknotes stacked, to ensure the accuracy of the counting.
An existing thickness detection device consists of two parts, which are respectively a detected body part and a sensor detection part. The principle of thickness detection is that: when a sheet-type medium (for example a banknote) to be detected passes through a thickness detection device, the thickness of the banknote causes variation of a distance between the detected body and a sensor. This variation of the distance causes variation of a detection physical quantity, and accordingly, the sensor outputs an electric signal corresponding to the variation. The varied electric signal, after being amplified by an amplifier, is transmitted to a subsequent processing circuit consisting of a micro-processor or a hardware circuit to be processed. Then, it is determined whether the thickness of the passing sheet-type medium meets the standard, to determine whether a surface of the sheet-type medium is adhered with a foreign matter, whether the banknote is a single sheet, and the like.
A common banknote thickness detection device has a structure as shown in FIG. 1, and the working principle thereof is described as follows.
Multiple driven wheel assemblies 008 are mounted on an assembly shaft 005, and the assembly shaft 005 is mounted on a module frame 001. A driving shaft 004 is mounted on the module frame 001 by flange bearings 011. Leaf springs 006 are mounted on the module frame 001 by a pressing plate 007 and screws 009. The leaf springs 006, after being deformed, apply a pressure on the multiple driven wheel assemblies 008, and the pressure may drive the multiple driven wheel assemblies 008 to fit the driving shaft 004 to form a passage for conveying a banknote 010. Power transmitted from outside acts on a driving wheel 003 mounted on the driving shaft 004, to drive the driving shaft 004 to rotate. The driving shaft 004 drives bearings on the driven wheel assemblies 008 which is in contact with the driving shaft 004 by friction, to generate a power for conveying the banknote 010. A signal detection plate 002 is mounted on an upper portion of the module frame 001.
FIG. 2 shows a working state of the above device. After the multiple driven wheel assemblies 008 and the driving shaft 004 are mounted, the leaf spring 006 in a free state may be changed into a deformed leaf spring 013 in a working state. The deformed leaf spring 013 applies an action force on the driven wheel assembly 008, thereby applying an action force on the driving shaft 004 in contact with a driven wheel 016 via the driven wheel 016 and forming a passage 017 for conveying the banknote 010. The direction of the passage 017 is determined by an action force 014 acting on the driving wheel 003 transmitted from outside, and the passage 017 may be a bi-directional passage. The driven wheel 016 is in contact with the driving shaft 004 to form a thickness detection point 018. When the banknote 010 is conveyed along the passage 017 and passes the thickness detection point 018, the variation of the banknote 010 in the thickness direction may be detected by the signal detection plate 002 via a height variation of a thickness measurement block 015. The multiple driven wheel assemblies 008 may cover the banknote 010 in the length direction of the banknote, and all the thickness variations of the banknote 010 may be detected as time passes and are converted into a thickness image by the signal detection plate 002 to be transmitted to an external identification system, and the thickness information of the banknote is processed.
The above banknote thickness detection device has the following issues: the thickness measurement block 015 is fixed on the driven wheel assembly 008, and the driven wheel assembly 008 rotates about the component shaft 005, a displacement generated by the thickness measurement block 015 has components in two directions, i.e., a displacement in the banknote thickness direction and a displacement in the banknote moving direction. Since the displacement in the banknote moving direction may adversely affect the detection result of the signal detection plate, the electric signal outputted by the sensor is not accurate. This error is just caused by the displacement of the thickness measurement block 015 in the banknote moving direction. A gap 012 exists between two driven wheels 016 mounted in the driven wheel assembly 008, as shown in FIG. 3. When the banknote 010 passes the detection point 018, the thickness of a portion, corresponding to the gap 012, of the banknote cannot be detected, therefore, the above banknote thickness detection device cannot detect the thickness of the full banknote.
A technical issue to be addressed by the present application is to overcome the deficiencies described above, to provide a thickness detection device for a banknote, in which a detected body only has a displacement in the thickness direction, and a thickness of the full banknote can be detected.